To satisfy ever-increasing demands for wireless data traffic, wireless communication systems have been developed toward higher data rates. Previously, efforts were expended on increasing spectral efficiency in order to increase data rates. However, as demands for traffic have been accelerated due to increased demands for smartphones and tablet Personal Computers (PCs) and the resulting rapid growth of application programs requiring a large amount of traffic, it is difficult to satisfy the soaring demands for wireless data traffic simply by increasing spectral efficiency.
One approach to averting the problem is to use a very broad frequency band. Because it is difficult to secure a broad frequency band in the frequency band below 10 GHz used for legacy cellular mobile communication systems, the broadband frequency should be obtained from a higher frequency band. However, as wireless communication is conducted in a higher transmission frequency, propagation path loss is increased. The resulting shortened propagation distance reduces service coverage. One of significant techniques to mitigate path loss and increase the propagation distance of waves is beamforming.
There are two types of beamforming, transmission beamforming at a transmitter and reception beamforming at a receiver. Transmission beamforming increases directivity by focusing signals transmitted from a plurality of antennas toward a specific direction (i.e. space). A set of plural antennas is called an array antenna and each antenna included in the array antenna is called an antenna element or an array element. Various antenna arrays are available, including a linear array and a planar array. Owing to its advantages of increased directivity and almost non-transmission of a signal in directions other than a specific direction, the transmission beamforming reduces interference with other users significantly.
Reception beamforming is available on the part of a receiver using a reception array antenna. The reception beamforming focuses wave reception toward a specific direction, thereby increasing the reception sensitivity of a signal from the specific direction and excluding signals from other directions. Therefore, interference signals are blocked.
To secure a broad frequency band, an extremely high frequency system, namely a millimeter wave system has been introduced. The wavelength of a signal wave gets shorter in a higher transmission frequency. If antennas are configured at half-wavelength intervals, more antennas may be arranged in the same area in an array antenna. That is, beamforming is favorable to a millimeter wave communication system because high-frequency beamforming can produce a higher antenna gain than low-frequency beamforming.
Beamforming basically requires a beam selection technique in which a Base Station (BS) and a Mobile Station (MS) accurately measure transmission and reception beams and report best beams. However, when the MS transmits a UL contention-based access channel to the BS, the beam selection process may already be completed or should be performed again under circumstances. Accordingly, there exists a need for a procedure of transmitting and receiving a UL access channel and a channel structure, which can support such cases.
The above information is presented as background information only to assist with an understanding of the present disclosure. No determination has been made, and no assertion is made, as to whether any of the above might be applicable as prior art with regard to the present invention.